Conventionally, in a radio communication system, when a communication terminal apparatus such as a cellular telephone or the like starts radio communication, the communication terminal apparatus receives a pilot signal periodically transmitted from a base station apparatus, and transmits an access request signal subjected open-loop transmission power control (OL-TPC) based on reception quality of the pilot signal to the base station apparatus using a random access channel (RACH). Then, when receiving the access request signal, the base station apparatus transmits an access permission signal to the communication terminal apparatus.
FIG. 1 schematically illustrates a configuration of a conventional radio communication system. The radio communication system as shown in FIG. 1 is comprised of base station apparatus 11 and a plurality of communication terminal apparatuses 12. Further, among the plurality of communication terminal apparatuses 12, communication terminal apparatus 12-1 is assumed to be positioned near base station apparatus 11 and in a good reception state. Meanwhile, communication terminal apparatus 12-2 is assumed to be positioned near a boundary of a communication area by base station apparatus 11, namely near a cell edge.
FIG. 2 illustrates radio signals on the time series transmitted and received between communication terminal apparatus 12 and base station apparatus 11 when communication terminal apparatus 12 starts radio communication. As shown in FIG. 2, first, base station apparatus 11 transmits a pilot signal with certain power to a plurality of communication terminal apparatuses 12 using a common pilot channel (CPICH) on downlink.
Next, when receiving the pilot signal, communication terminal apparatus 12 transmits an access request signal with transmission power associated with the reception quality (reception power of the pilot signal on the CPICH in FIG. 2) to base station apparatus 11 using a random access channel (RACH) on uplink. Resources used as a sub-channel of the RACH are predetermined such as, for example, timing, channelization code, subcarrier and the like, and communication terminal apparatus 12 randomly selects one from the predetermined resources in transmitting the access request signal.
Subsequently, when receiving the access request signal, base station apparatus 11 transmits an access permission signal with certain power to communication terminal apparatus 12 using a forward access channel (FACH). Then, when receiving the access permission signal, communication terminal apparatus 12 transmits a data packet with transmission power associated with the reception quality of the pilot signal to base station apparatus 11 using a data channel on uplink. In addition, in FIG. 2, the down arrow represents downlink, while the up arrow represents uplink, in each channel.
Further, as well as the conventional technique as described above, a technique is developed that communication terminal apparatus 12 first transmits a short packet called preamble to base station apparatus 11 while increasing the transmission power gradually, and when base station apparatus 11 detects the preamble, communication terminal apparatus 12 transmits an access request signal to base station apparatus 11 (for example, see Patent Document 1).    Patent Document 1: Japanese Patent Application Laid-Open No. 2002-528997